# Charging by Friction & Contact

## Purpose:

* to observe, describe and explain:

• charging by friction and contact
• evidence for two kinds of electrical charge

Note: You may work with one or two partners for this activity. Discuss the explanations and answers with your partner(s) and write one clear, accurate answer on another sheet of paper. Be sure that all participants put their name on this sheet.

## plastic strips cloth scraps 2 pith balls with thread ring stand ring stand clamp tape Description:

### Part 1 - A Single Pith Ball

1. Hang a single pith ball from a ring stand clamp using a small piece of tape.
2. Charge a plastic strip by rubbing with a cloth scrap.
3. Bring the charged strip close to but not touching the pith ball. Describe what happens.
4. Allow the pith ball to touch the charged strip. What happens now? Why does the pith ball do that?
5. After you touch the pith ball with your hand, how does it behave? Why?
6. Devise a test to tell whether your plastic strip has a positive or a negative charge and write a short description. (You may borrow a plastic rod and fur pad or glass rod and silk cloth from your teacher for this test.) Carry out your test. Is the plastic strip positively or negatively charged?
7. See if you can find a combination of plastic strip and cloth that will produce the opposite charge from your original strip. (You may use your own object, such as a comb, etc. if you wish.) How do you know that it is oppositely charged?

### Part 2 - Two Pith Balls

1. Hang a second pith ball next to your original so that they are touching when they are at rest.
2. Charge both pith balls with your plastic strip. What happens? Why?
3. If you bring the charged strip close to the two charged pith balls without touching them, what happens? Why?
4. If you bring an oppositely-charged strip near the charged pith balls without touching them, what happens? Why?